The different message block while in a 1P list is odd and I don't think I've seen anyone reporting this before. Can you take a picture if it happens again?[UPDATE]
The "Emergency Alert" came up again, this time while I was watching live TV. But the display was different. In both cases there was a marching banner with the message surrounded in the middle with a message saying it was an emergency alert atop the banner and a message saying the alert would go away automatically below the banner.
In the case of viewing the 1p list, the 1p list was replaced by a 4 page message block which scrolled through the 4 pages. The content of the pages was essentially the same as the marching banner. This bit was not present when the alert came up on live TV.
In the live TV case, the banner and messages did go away on their own. In the case of the 1p, the 4 page display changed to a notice that I could now re-tune the station I was watching. But (presumably) since I was not really watching a station I was stuck at that point and had to power off the Roamio+